Tire Inflation

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Welcome to any new FMCA members. If you have questions on tires you should check out the TIRE thread in the Technical area.

Until then here are the general recommendations

I do not see posts with actual side to side measured loads on each tire.
Single axle trailers should:

1. Confirm actual load on each tire
2. Calculate 115% of the heavier end
3. Check Load & inflation tables using the 115% number to learn the MINIMUM allowable inflation
4. Add 10% to that inflation number and use this new number for your goal Cold Inflation psi

Multi-axle trailers should:
1. Confirm actual loads for each tire
2. Calculate 115% of the heavier end
3. Check Load & inflation tables using the 115% number to learn the MINIMUM allowable inflation
4. Add 10% to that inflation number and use this new number for your goal Cold Inflation psi
5. If you want to lower the potential for a belt separation due to the multi-axle Interply Shear increase your CIP to the tire sidewall pressure.

This link is a Google search on Interply Shear if you want to learn more.

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How in the world do they determine if the tires are inflated to sidewall pressure. Is there a little gremlin with a report card in each tire. Some manufactures just never get out of the box.

Their logic would be that if the tire had been inflated to the sidewall pressure noted on the outside of the tire, the tire wouldn't have blown out with the low mileage and nearly new manufacture date on it.

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Yes, the door placard is based on each axle being loaded to GAWR. That is NOT an assumption you want your life riding on. And, a LONG Class C is one of the more prone to being overloaded, so weighing is even more important.

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I know that it can be frustrating, with weight. I have a large diesel coach and my decision, had nothing to do with what I could tow or carry! My 8 tires are rated for 125psi cold, I carry 115 cold, based upon my weight. I had 105 psi cold, before I started traveling with my Lady in the coach. She also has a DP.

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Not sure if this thread was intended for the TT section or not, but I have a response intended for TT's. I'm reasonably sure that there is also a speed rating on TT tires, and I would bet that it is not 80+ MPH, I have fifth wheelers especially pass me on highways that I usually drive 65 to 70 on, some are moving 80+ MPH I feel pretty sure because they pass like I'm sitting still. Many times I pass them on the side of the road with a blown tire.

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Many TT and 5th wheel owners change out the tires to truck tires with a higher MPH rating.

I have actually read about this on TireMan's website. I'm one of those people that when free knowledge is present I read up on it.

This is not a good idea as a light truck tire is not designed to scrub where a trailer service tire is. When you think about it, makes sense, trailer axles do not steer so they will scrub in tight or not even so tight maneuvers. Sidewall construction is not designed for this application.

I had two service trailers when I owned the mobile truck service business, both trailers wore out the tires at the 9 year mark, not once did I experience any tire failures. They both also had cheap Chinese tires on them. I truly believe most of those failures are not the tires fault! I will admit neither of them ever broke the 65mph speed limit on the tires and they were loaded to the max GVWR. I also made certain the trailers were level (parallel to the ground) when coupled to the trucks.

I'm sure he can go into a better description on the scrubbing differences in tire design.

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I have fifth wheelers especially pass me on highways that I usually drive 65 to 70 on, some are moving 80+ MPH I feel pretty sure because they pass like I'm sitting still. Many times I pass them on the side of the road with a blown tire.

YUP, its a game with us to see how long until they are on the side of the road with a destroyed tire or upside down in the shoulder. I always laugh and tell my wife "tomorrow there will be one more post on the web blaming the tire manufacture for that failure".

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Their logic would be that if the tire had been inflated to the sidewall pressure noted on the outside of the tire, the tire wouldn't have blown out with the low mileage and nearly new manufacture date on it.

You pretty-well summed up the Carlisle tire warranty. That's why I stopped buying them, how are you going to contest a "you ran them underinflated" warranty that includes bulges, etc? BTW, that inflate to sidewall pressure clause is gone now.

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Unless it was a bad tire, had been run flat previously, and most likely a bunch of other possibilities. At the time of a blow out there is no way they would know other than by assumption.

Yes, most probably operator error, but only assumptions.

1

Sorry, Wayne but there are ways to identify the probable inflation & load history of a tire. Just as a Medical Examiner can do an autopsy and identify the signs of bad diet and poor or no exercise, or years of smoking, it is many times possible to see the external signs of low inflation and high load. These signs can show up in the indentation into the tire left by the wheel. Also, the different flex markings can be seen on the interior of a tire.

Manufacturing "Defects" will usually result in early life failure i.e. <1,000 miles. Tire failure is in itself not proof of some nebulous "defect" even though lawyers and those not experienced in failed tire inspection want to think so.

Once you examine, in detail, a few thousand tires from both controlled testing and from day to day use & abuse the conditions seen in tires tell a story of the tire's history.

Too often people simply think of the conditions (load, speed, inflation, road) at the moment the tire fails as the "facts" to be considered when trying to decide the "why" a tire failed. In reality, the damage might have been done hours, days or even months earlier. As I point out in my RV Tire Knowledge Seminars at FMCA Conventions, tires are like potato salad, putting the salad back in the refrigerator after it was left for hours in the hot sun does not "fix it" and make it good to eat the next day any more than taking the burnt hot dog off the grill and letting it cool down before serving it makes for a good meal. Adding the correct air in a tire after running it low for thousands of miles does not repair the damage. Slowing down to 50 after hours of 70 to 80 over the preceding weeks and months does not "fix" or heal the thousands of microscopic cracks that were formed in the overheated and overstressed belt rubber. If a person stopped his smoking addiction of 2 packs a day for 40 years a couple months ago, will his lungs be clean and clear today?

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Roger,
Thanks for the reply, I do understand what you are saying. Unfortunately I'm not an engineer and I have to look at the simple things and I am not able to perform forensic investigation on a tire. Now, if it is a computer I can do forensic investigation or could when I was an IT Security Specialist,

A few years ago I posted a zipper blow out on an inside dual. Same dual that was flat in my driveway after taking it out of storage. It was 1000 miles or later that the blow out occurred, I replaced both duals on that side knowing that most likely the other may have weakened,

I enjoy your blog, Thanks

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I thought I was being smart when I replaced my d rated tires with e rated tires. It wasn't until I mounted them on my tt that I realized my aluminum wheels are only rated to 65psi. So now I've got e rated tires that are not inflated up to thier max psi(80)/load capacity.

Is an e load tire inflated to 65psi better or worse than a d load tire inflated to 65?

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I thought I was being smart when I replaced my d rated tires with e rated tires. It wasn't until I mounted them on my tt that I realized my aluminum wheels are only rated to 65psi. So now I've got e rated tires that are not inflated up to thier max psi(80)/load capacity.

Is an e load tire inflated to 65psi better or worse than a d load tire inflated to 65?

Edit:

I have a tandem axle tt with a 9800lb gvwr

There is no problem running a LR-E at 65 psi if that is the rating for your wheels. BUT

Simply stating the GVWR is no indication of the actual load on the tires.

I have covered proper inflation of Trailer tries a number of times, in detail in my Blog. Basically, run the inflation on the tire sidewall. BUT in your case, that would be 65 psi.

You also need to confirm your actual load is less than 85% of the Max load capacity for your size tire (at 65 psi). or 2,083# on the heaviest loaded tire.

You can PM me if you need clarification for your situation.

BTW, when you upgraded your tires did you get bolt in metal valves installed too?

Truth be told I've never weighed the trailer and have no idea if the extra capacity is needed. Spending 160$ on new wheels that give me an extra 1200# capacity seems worth it regardless. I think I'm going to buy the above wheels before we start our second cross country trip next month.